Timing of Excess Weight Gain in the Avon Longitudinal Study

OBJECTIVES: To test the hypothesis that most excess weight gain occurs by school entry in a large sample of English children, and to determine when the greatest gain in excess weight occurred between birth and 15 years.

METHODS: Longitudinal data were collected annually from birth to 15 years in 625 children. Weight and BMI at each time point were expressed relative to UK 1990 growth reference as z scores. Excess weight gain was calculated as the group increase in weight and BMI z scores between specific time periods.

RESULTS: Weight z score did not increase from birth to 5 years (mean difference: 0.04 [95% confidence interval (CI): −0.03–0.12] P = .30) but increased from 5 to 9 years (mean difference: 0.19 [95% CI: 0.14–0.23] P < .001). BMI z score increased from 7 to 9 years (mean difference: 0.22 [95% CI: 0.18–0.26] P < .001), with no evidence of a large increase before 7 years and after 9 years.

CONCLUSIONS: Our results do not support the hypothesis that most excess weight gain occurs in early childhood in contemporary English children. Excess weight gain was substantial in mid-childhood, with more gradual increases in early childhood and adolescence, which indicates that interventions to prevent excess weight should focus on school-aged children and adolescents as well as the preschool years.